(a) Field of the Invention
The present invention relates to a device for detecting positions of samples applied onto a carrier being shifted in a definite direction, and more specifically to a sample detector used for quantitative analyses of fractionated patterns of sera in electrophoresis.
(b) Description of the Prior Art
In the electrophoresis, samples are applied onto a carrier made of cellulose acetate paper or similar material and fractionated patterns of the samples are formed by electrically energizing the carrier. Then, the carrier is colored, discolored and made transparent by being dipped into a clarifying liquid, whereafter the fractionated patterns are quantitatively analyzed with a colorimeter. For automatic quantitative analyses of the sample applied onto the carrier with a colorimeter, the carrier is shifted between a light source and a photodetector, the carrier is stopped when a sample on the carrier is located right between the light source and photodetector, and the light source and photodetector are moved in the direction perpendicular to the shifting direction of the carrier to scan the sample for carrying out photometry. Such a photometric apparatus requires a sample detector which precisely detects a sample on the carrier to be subjected to photometery when it is located right between the light source and photodetector.
FIG. 1 shows the construction of an example of the conventionally known sample detectors. In this drawing, the reference numeral 1 represents a carrier, the reference numeral 2 designates fractionated patterns of samples applied at constant intervals on the carrier, the reference numeral 3 denotes a photometric light source assembly consisting of a light source lamp 4, a lens system 5, a filter 6, a slit plate 7, etc., the reference numeral 8 represents a photometric detector assembly consisting of a slit plate 9 and a photodetector element 10, the reference numeral 11 designates optical fibers having ends arranged in a row under the carrier passage and in the direction perpendicular to the shifting direction of the carrier as shown in FIG. 2, the reference numeral 12 denotes a light source lamp arranged at the other ends of the optical fibers 11, and the reference numeral 13 represents a plural number of photodetector elements arranged over the carrier passage for receiving light emerging through the optical fibers 11 from the light source lamp 12. These optical fibers 11, light source lamp 12 and photodetector elements 13 compose a sample detector.
When the carrier 1 is shifted in the direction indicated by the arrow A for photometry of samples in the photometric apparatus having the above-described construction, the light emerging from the optical fibers 11 pass through the carrier 1 and are received by the individual photodetector elements 13. The photodetector 13 provide high outputs when a transparent portion 1a of the carrier 1 corresponds to the position of the sample detector, and low outputs when the sample 2 applied onto the carrier 1 corresponds to said position. It is therefore possible to carry out photometry of the sample by stopping the shifting of the carrier 1 when the sample on the carrier is detected and shifting the photometric unit consisting of the light source assembly 3 and photometric detector 8 in the direction perpendicular to the shifting direction A of the carrier.
In the conventional sample detector having the above-described construction, each of the photodetector elements requires a preamplifier for processing signals obtained from the detector element, or highly priced preamplifiers having high imput impedance and low drift for signal processing with higher accuracy. Therefore, the conventional sample detector is unavoidably highly priced. In order to correct this defect, it is conceivable to use a single preamplifier in the conventional sample detector. For this purpose, however, it is necessary to use a single detector element which must have a photo sensitive area large enough to cover the end surfaces of many optical fibers at a time. Using a larger photosensitive area unavoidably increases dark current and drift, thereby degrading analytical accuracy. Furthermore, it is conceivable to use a single preamplifier in combination with a plural number of detector elements, but such a method requires a control circuit which selects a detector element to be connected to the preamplifier.